The present invention relates to continuously variable transmissions of the toroidal type for use as, for example, automotive transmissions or transmissions for various industrial machines, and more particularly, to an improvement of a synchronous cable for synchronously rotating at least a pair of power rollers stored in a continuously variable transmission of the toroidal type.
FIGS. 15A and 15B show a continuously variable transmission of the toroidal type as a known example of an automotive transmission. This transmission comprises an input disc 2 mounted on an input shaft 1, an output shaft 3 coaxial with the input shaft 1, and an output disc 4 fixed to an end portion of the output shaft 3. Trunnions 6a and 6b, which can rock around their corresponding pivots 5, are arranged inside a casing (not shown) that contains the continuously variable transmission.
A displacement shaft 7 is provided in the central portion of each of the trunnions 6a and 6b. When the trunnions 6a and 6b are rocked individually around the pivots 5, the tilt angle of each shaft 7 changes. A power roller 8 is rotatably supported on each shaft 7. The power roller 8 is located between the input and output discs 2 and 4. Opposite inner surfaces 2a and 4a of the discs 2 and 4 are concave surfaces that are obtained as circular arcs around the pivots 5 are rotated individually around the shafts 1 and 3. A peripheral surface 8a of each power roller 8 is a spherical surface, which is contact with the respective inner surfaces 2a and 4a of the discs 2 and 4.
A push device 9 of the loading-cam type is provided between the input shaft 1 and the input disc 2. The device 9 elastically presses the input disc 2 toward the output disc 4. The device 9 includes a cam plate 10 rotatable together with the input shaft 1 and a plurality of (e.g., four) rollers 12 that are held by means of a holder 11. A cam surface 13 is formed on one surface (on the right-hand side of FIG. 15A) of the cam plate 10. The cam surface 13 has undulation in the circumferential direction of the plate 10. An undulating cam surface 14 is also formed on the other surface (on the left-hand side of FIG. 15A) of the input disc 2. The rollers 12 are rotatably supported by means of shafts that extend radially from the input shaft 1.
When an engine is actuated, the cam plate 10 in the continuously variable transmission of the toroidal type with the above-described construction rotates together with the input shaft 1. Thereupon, the rollers 12 are pressed against the cam surface 14 of the input disc 2 by means of the cam surface 13. In consequence, the input disc 2 is pressed against the power rollers 8, and the cam surfaces 13 and 14 are connected to the rollers 12, whereupon the input disc 2 rotates. The turning effort of the input disc 2 is transmitted to the output disc 4 through the power rollers 8, whereupon the output disc 4 and the output shaft 3 rotate.
The rotations of the input and output shafts 1 and 3 can be slowed down by tilting the displacement shafts 7 so that the respective peripheral surfaces 8a of the power rollers 8 are individually in contact with portions which are near the central of the inner surface 2a of the input disc 2 and portions which are near the outer peripheral of the inner surface 4a of the output disc 4, as shown in FIG. 15A. On the other hand, the rotations of the input and output shafts 1 and 3 can be speeded up by rocking the trunnions 6a and 6b in the opposite direction, as shown in FIG. 15B. Further, a transmission ratio intermediate between those for the speed reduction and increase modes can be obtained by adjusting each displacement shaft 7 to a tilt angle intermediate between the ones shown in FIGS. 15A and 15B.
A synchronous cable 100 is passed around the respective peripheral surfaces of end portions of the trunnions 6a and 6b. As shown in FIG. 16, the cable 100 includes a wire rope 101 in the form of an endless loop and a pair of metallic retainers 102 that are fixed to the rope 101 in opposite positions. In incorporating the cable 100 into the continuously variable transmission of the toroidal type, the wire rope 101 is twisted to cross in the shape of the figure "8", as indicated by two-dot chain lines in FIG. 17. Then, the retainers 102 are fitted individually into retainer mounting portions of the trunnions 6a and 6b. By doing this, the synchronous cable 100 and the trunnions 6a and 6b can be caused to engage one another without slippage.
The synchronous cable 100 serves to synchronize the respective tilting or rocking motions of the trunnions 6a and 6b around their corresponding pivots 5. More specifically, the cable 100 functions as safety means for synchronously tilting the trunnions 6a and 6b in case of failure of an actuator (hydraulic drive unit) for tilting the trunnions. With use of the synchronous cable 100, excessive frictional force can be prevented from acting between the inner surfaces 2a and 4a of the discs 2 and 4 and the respective peripheral surfaces 8a of the power rollers 8, so that the continuously variable transmission can avoid being fatally damaged. Even in case of such failure, moreover, the transmission can secure its minimum power transmitting function.
As the conventional synchronous cable 100 is incorporated into the continuously variable transmission of the toroidal type, its shape is changed into the shape of the figure "8" in a manner such that the simple loop shown in FIG. 16 is twisted by means of external force. Accordingly, the conventional cable 100 is restored to the simple loop, as shown in FIG. 16, if the external force is removed. In incorporating the cable 100 into the continuously variable transmission, therefore, the wire rope 101 must be subjected to the external force to maintain its 8-shaped form, as indicated by two-dot chain lines in FIG. 17, as the retainers 102 are fitted individually into the retainer mounting portions of the trunnions 6a and 6b. This operation is troublesome and constitutes a hindrance to efficient assembling of the continuously variable transmission of the toroidal type.
Further, the conventional synchronous cable 100 has the following drawbacks to be improved. In the cable 100, the retainers 102, formed of metallic tubes, are fitted on the opposite end portions and middle portion of the wire rope 101, and are fastened to the rope 101 by being caulked throughout their overall length L. If the actuator for driving the trunnions 6a and 6b gets out of order, a force of hundreds of kgf may act on the synchronous cable 100, in some cases. Therefore, the rope 101 and the retainers 102 must be firmly fixed to one another. However, the conventional synchronous cable involves the following problems.
(1) Since the metallic tube as the material of each retainer 102 must be fixed to the wire rope 101 by being caulked throughout the overall length L, it is formed of gun metal (copper alloy such as Cu--Sn or Cu--Sn--Zn) that is lower in hardness than iron. Owing to the softness of gun metal, however, the strength of the retainers 102 cannot be enhanced. If a substantial tensile load acts on the rope 101, therefore, the retainers 102 may possibly be disengaged from the rope 101.
(2) Since the end faces of the retainers 102 are brought heavily into contact with the retainer mounting portions of their corresponding trunnions 6a and 6b, they are easily worn or deformed, sometimes producing substantial backlash between them. The synchronous cable 100 must serve to equalize the respective tilts of the power rollers 8 in case of failure of the actuator. If the backlash between the trunnions 6a and 6b and the retainers 102 is too much, however, it is hard to equalize the tilts of the rollers 8.
(3) If each retainer 102 is caulked throughout the overall length L, the resulting outline of each end portion thereof becomes smaller than the previous one (indicated by two-dot chain line in FIG. 18). In consequence, the cross-sectional areas of contact portions between the retainer mounting portions of the trunnions 6a and 6b and the retainers 102 are reduced, so that the contact pressure increases. Thus, the retainers 102 can be worn or deformed more easily.